Un-patched bug could put 500m Android phones in a coma

Security researchers have disclosed details of a bug affecting 500 million Android phones that could render them “apparently dead”, making it a useful tool for ransomware attackers.

The bug comes on the heels of the so-called Stagefright bug that could allow an attacker to compromise all the world’s one billion Android phones with a malicious text message.

While Google took quick steps to patch Android’s source code — which handset vendors may or may not release in a firmware update — the company hasn’t patched this one some three months after it became aware of it.

Researchers at Trend Micro who discovered and reported the flaw to Google in mid-May said the Android maker considered it a low priority flaw.

Nonetheless, Trend Micro researcher Wish Wu points out the bug can be exploited to leave a phone unable to make calls, by knocking out the ring tone, text tone, and notifications and leave it with a “lifeless screen”.

The phone won’t be completely bricked, but without these functions a user wouldn’t know if a call was coming in and couldn’t even accept it if they somehow knew. It may also make the UI sluggish or completely non-responsive and if the phone is locked, it can’t be unlocked.

The good news for Android users is that unlike Stagefright, the bug requires some user interaction to be exploited, including installing a malicious app or by visiting an attack site.

Despite this, Wu points out that there are plenty of methods to dupe users into doing this, including repackaging a popular real app or luring victims to an attack site. The fact it can be used to freeze a phone in lock status may offer ransomeware attackers more leverage over victims.

“In addition to encrypting on the device being encrypted, the device itself would be locked out and unable to be used. This would increase the problems the user faces and make them more likely to pay any ransom,” he noted.

The flaw is located in an Android service called mediaserver where media files on a device are indexed. The flaw affects Android 4.3 Jelly Bean through to Android 5.1.1 Lollipop, the latest version, which account for just over half of all Android devices that connect to the Google Play app store, not including the millions that don't.

“This service cannot correctly process a malformed video file using the Matroska container (usually with the .mkv extension). When the process opens a malformed MKV file, the service may crash (and with it, the rest of the operating system),” said Wu.

Wu said that in the case the flaw is exploited with a malicious app — that is, one with a malformed embedded MKV file that registers itself to auto-start when the device boots — would cause the OS to crash every time the device is switched on.

Trend Micro has developed a proof of concept for the flaw, and demonstrates the attack using a malicious website in this video.

The company said Google on May 20 acknowledged its report as a "low priority vulnerability", which has been assigned the number ANDROID-21296336.

This article is brought to you by Enex TestLab, content directors for CSO Australia.

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